Image graphics are omnipresent in modern life. Images and data that warn, educate, entertain, advertise, etc. are applied on a variety of interior and exterior, vertical and horizontal surfaces. Nonlimiting examples of image graphics range from advertisements on walls or sides of trucks, to posters that advertise the arrival of a new movie, to warning signs near the edges of stairways.
Image graphics are increasingly made using digital techniques. Among popular digital techniques are electrographic processes and ink jet printing.
Electrographic printing processes can use dry or liquid toners. Electrographic printing processes can employ either (a) electrophotographic printers where the means of imaging consists of applying a latent charged image to a drum, developing this image with a toner and transfering this to paper or film or (b) electrostatic printers where a nib array writes a latent image on a dielectic coated paper or film which then passes a series of toning stations to generate a visible image.
Conventional liquid toner comprises pigmented resin particles, isoparaffinic hydrocarbon carrier liquid (such as Isopar.TM. branded liquid), and charge control agent to effect electrical properties. Although pigment, resin, and charge control agent will each be present in the liquid toner, proper toning of the latent image occurs only when the toner particle is composed of all three components.
Nonlimiting examples of commercial electrostatic printers are multi-pass and single-pass electrostatic printers, such as those marketed by Raster Graphics of Sunnyvale, Calif., the ColorgraiX division of Xerox Corporation of San Jose, Calif., Minnesota Mining and Manufacturing Company (3M) of St. Paul, Minn., and Nippon Steel Calcomp Corporation of Tokyo, Japan. 3M markets a number of media, toners, and overlaminates under the Scotchprint.TM. brand to be used in electrostatic printing. 3M also markets Graphic Maker Electrostatic Printing software useful in converting digital images from the Internet, ClipArt, or Digital Camera sources into signals to electrostatic printers to print such images.
The use of thermal and piezo ink jet inks have greatly increased in recent years with accelerated development of inexpensive and efficient ink jet printers, ink delivery systems, and the like.
Thermal ink jet hardware is commercially available from a number of multinational companies, including without limitation, Hewlett-Packard Corporation of Palo Alto, Calif., USA; Encad Corporation of San Diego, Calif., USA; Xerox Corporation of Rochester, N.Y., USA; LaserMaster Corporation of Eden Prairie, Minn., USA; and Mimaki Engineering Co., Ltd. of Tokyo, Japan. The number and variety of printers changes rapidly as printer makers are constantly improving their products for consumers. Printers are made both in desk-top size and wide format size depending on the size of the finished image graphic desired. Nonlimiting examples of popular commercial scale thermal ink jet printers are Encad's NovaJet Pro printers and H-P's DesignJet 650C, 750C, 2500CP, and 3500CP printers. Nonlimiting examples of popular desk-top thermal ink jet printers include H-P's DeskJet printers and OfficeJet printers.
3M also markets Graphic Maker Ink Jet software useful in converting digital images from the Internet, ClipArt, or Digital Camera sources into signals to thermal ink jet printers to print such images.
Ink jet inks are also commercially available from a number of multinational companies, particularly 3M which markets its Series 8551; 8552; 8553; and 8554 pigmented ink jet inks. The use of four principal colors: cyan, magenta, yellow, and black permit the formation of as many as 256 colors or more in the digital image.
Media for ink jet printers are also undergoing accelerated development. Because ink jet imaging techniques have become vastly popular in commercial and consumer applications, the ability to use a personal computer to print a color image on paper or other receptor media has extended from dye-based inks to pigment-based inks. And the media must accommodate that change. Pigment-based inks provide more brilliant colors and more durable images because pigment particles are contained in a dispersion before being dispensed using a thermal inkjet print head.
Ink jet printers have come into general use for wide-format electronic printing for applications such as, engineering and architectural drawings. Because of the simplicity of operation and economy of ink jet printers, this image process holds a superior growth potential promise for the printing industry to produce wide-format, image-on-demand, presentation-quality graphics.
Image quality is what the viewing public and paying customers will want and demand to see. From the producer of the image graphic, many other obscure demands are also placed on the ink jet media/ink system, or electrostatic media/toner system, from the print shop. Also, exposure to the environment can place additional demands on the media and ink (depending on the application of the graphic).
Image quality must outlast the intended duration of the image graphic in its placement, i.e., the image graphic must be durable in its intended environment. For example, it is expected that an outdoor image graphic adhered to the side of a tractor trailer must maintain its image quality for as much as seven to ten years, while the trailer travels through all types of inclement and sometimes brutal weather conditions. Often, it is a combination of ultra-violet light, heat, humidity, cold, wind, and other environmental extremes that causes a beautiful image to succumb to these natural elements that cause image fading or other weathering effects. Stabilizing agents (e.g., ultra-violet light absorbers, ultra-violet light stabilizers, antioxidants, heat stabilizers, and a variety of other additives) are often included in receptor media compositions to protect those media and the image on those media from weathering effects. The amount of the stabilizing agent can be limited by the composition or thickness of the film/membrane or solubility/compatibility of the stabilizing agents. This limit may be less than that required for the intended life of the graphic.
Often the image on the graphic is protected by the nature of the receptor media on which the image is printed if the media uses such stabilizing agents, regardless of the printing method described above. But more often, particularly for extremely durable image requirements, clear overlaminates are adhered to, or clear coatings cover, the image graphic.
Overlaminate films or clear coatings (also known as "clears" in the graphics industry) are expensive to produce and are limited in types of materials because of the clarity required for the exposed layer in the final, protected image graphic. Overlaminates and clears need the same environmental protection as the remainder of the graphic and often require more intense protection because of the purpose of the overlaminate or clear to protect and the requirement of continued clarity during image graphic placement for long durations of time.